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# Building a vibration sensor

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#### mmilbury

##### New Member
I'm building an acceleration sensor for a project with low g's. (.05<g<1.0 max g = 2.0) I've researched several sensors on the web and have selected a sensor with a sensitivity of 120 pV/g.

My understanding is there is a known mass that reacts to the vibration. This reaction is output as a certain voltage. What I am attempting to do is interface my accelerometer with a circuit board.

Would anybody know how I would do this? I would like to make a direct connection to the ADC without using an amplifier circuit. With this in mind, what would be the best way to do this? If I go as high as 2.0g's would you know how I could limit this voltage to keep it from overloading the processor?

Any help would be greatly appreciated.

Hi,
just checking I understood right, since I've not been working with
acceleration sensors before.

Is the voltage output from a sensor really as low as 120 pV / g,
so at 2g you will only get 240 pV output ?
If that is correct, its quite small voltages you have to work with.
Even an 18 bit A/D converter has a resolution of about 1uV / LSB
and you would need something like 100.000 - 1000.000 times better resolution than that to get any data from your sensor.

It looks like a very good amplifier is needed between the sensor and the A/D converter.

Aren't there units with sensor and amplifier integrated that you could use ? They should have much higher output voltages, and their output could probably be fed stright into an A/D converter,
maybe amplified by a very simple amplifier first.

/Argonheart

Piezo-electric accelerometers

Mmilbury,
I believe there could be a mis-quote in your posting -- piezo-electric accelerometers produce Coulombs of charge as their output, not volts.
A typical industrial accelerometer will produce 25pC/g so if you meant charge, your 120pC/g unit is a massive output :shock:

One Coulomb is one amp.second [NOTE that is multiplying NOT dividing]
One amp is one Coulomb/second [This is dividing !]

Because of the extremely small energy levels involved, these devices are connected with 'charge cable' - a good quality sceened cable - to a 'charge amplifier' which produces around 100mV/g (fancy name, simple circuit!). Could this be what you meant? 120mV/g ?

It is impossible to connect directly from accelerometer to A/D, you must use a charge amp -- accelerometers are available (for a price!) that contain the charge amp and so give mV/g directly, but then they require power, usually over the same two wires as the signal, so some DC offset is involved (possibly 12 to 24v DC).

Hi I just would like to know what did u do at the en with your vibration sensor.I have to do a project about it and I was wondering if u could help me out...
Gabriella

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